For a long time, fumaric acid dialkyl esters as well as fumaric acid monoalkyl esters and salts thereof have been successfully used for treating psoriasis. Said use is described in a number of patents, for example EP-A-0 188 749, DE-95 30 327, DE 26 21 214 or EP-B-0 312 697.
The use of fumaric acid mono- or diesters is also described for the treatment of autoimmune diseases such as polyarthritis, multiple sclerosis (cf. DE 197 21 099.6 and DE 198 53 487.6), but also for use in transplantation medicine (cf. DE 198 53 487.6 and DE 198 39 566.3). The use of fumaric acid mono- and diesters for the treatment of NF-kappaB mediated diseases and the treatment of mitochondrial diseases is also known from the unpublished German applications DE 101 01 307.8 and DE 100 00 577.2. However, all the cited documents merely describe fumaric acid mono- and diesters, optionally in the form of certain salts, i.e. compounds wherein one or both acid functions of the fumaric acid are esterified with an alcohol.
Because of their volatility and sublimability, however, the above-mentioned fumaric acid esters have the disadvantage of being difficult to handle when preparing pharmaceutical products, especially those in solid form for oral administration. Specifically the preparation of such products requires protective measures such as the use of breathing masks, gloves, protective clothing.
In addition, the fumaric acid esters are absorbed in the gastro-intestinal tract after oral administration and taken up unspecifically from the bloodstream by all body cells. Therefore, it is necessary to administer high dosages in order to provide a therapeutically effective level of the active ingredient on or in the target cells.
Such high dosages in turn lead to the known side effects of a fumaric acid therapy like flush symptoms (reddening) or gastrointestinal irritation (nausea, diarrhoea, winds). Even though such side effects may be reduced considerably by administering the active ingredient in the form of micro-tablets as described in the above-cited prior art, they cannot be avoided altogether.
At the same time, the fumaric acid esters are rapidly hydrolysed in the blood and the products of said hydrolysis, alcohol and fumaric acid or fumaric acid monoester, metabolised. In order to maintain therapeutically effective levels repeated and frequent administration is therefore necessary. Even though a certain adaptation is observed concerning the side effects, a further reduction of the side effect rate would be desirable.